Genetic Analysis of Chinese Patients with Early-Onset Dementia Using Next-Generation Sequencing

Case of Autosomal Dominant Alzheimer Disease With Negative Findings From PiB-PET Examination

Background and Objectives

This study reports an uncommon case of autosomal dominant Alzheimer disease (AD) with negative PiB-PET findings.

Methods

A 55-year-old woman was admitted to the hospital due to a progressive cognitive decline for over 9 years, along with a possible dementia family history. The patient underwent routine laboratory tests, neuropsychological assessments, and neuroimaging examinations. Additionally, the cerebrospinal fluid sample was analyzed for AD biomarkers using the Single Molecular Array (Simoa) technique. A targeted Next-Generation-Sequencing (NGS) panel screening was also conducted.

Results

Routine blood and CSF laboratory tests, as well as CSF tap test, yielded negative results. Cranial MRI showed atrophy of the whole brain. PiB-PET scanning indicated that PiB was merely retained in her brain with an overall standard uptake value ratio (SUVR) <1.0. Simoa analysis showed an increase in the level of CSF t-tau and a decrease in that of CSF Aβ42. NGS panel screening detected a c.G2032A (p.D678N) heterozygous mutation in APP. Consequently, the patient was diagnosed with autosomal dominant AD.

Discussion

We have reported an uncommon case of autosomal dominant AD carrying p.D678N variant in APP with negative PiB-PET results. The diagnosis of AD should not be directly excluded solely based on the negative PiB-PET results.

Identification and functional characterization of novel variants of MAPT and GRN in Chinese patients with frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common cause of dementia after Alzheimer's disease, characterized by distinct changes in behavior, personality, and language. Our study performed whole exome sequencing and repeat-primed PCR analysis in 29 unrelated FTD patients. Consequently, 2 known pathogenic variants (MAPT: p.P301L; TBK1: p.I450Kfs), and 4 novel variants (MAPT: p.R406Q, p.D430H, p.A330D; GRN: c.350-2A>G) were identified. The functional analysis results showed that phosphorylated tau levels were higher in cells expressing p.R406Q and p.D430H tau than those expressing wild-type tau, especially at the Thr205, Thr231, and Ser396 phosphorylation epitopes. Besides, the p.R406Q and p.D430H variants of MAPT impaired the ability of tau to bind to the microtubules and increased tau self-aggregation. Furthermore, we found that the c.350-2A>G variant caused exon 5 skipping. Our results showed that p.R406Q, p.D430H, and c.350-2A>G variants were classified as pathogenic. Finally, we summarized the clinical characterization of patients carrying pathogenic variants of MAPT in the East Asia populations. Our results broaden the genetic spectrum of FTD with MAPT and GRN variants.

Clinical features and biomarkers of semantic variant primary progressive aphasia with MAPT mutation

BACKGROUND

Semantic variant primary progressive aphasia (svPPA) is generally sporadic, with very few reports of tau pathology caused by MAPT mutations.

METHODS

A 64-year-old man was diagnosed with svPPA with MAPT P301L mutation. Clinical information, cognitive and language functions, multimodal magnetic resonance imaging (MRI), blood biomarkers, fluorodeoxyglucose (FDG) imaging and tau positron emission tomography (PET) were obtained.

RESULTS

Semantic memory impairment was the earliest and most prominent symptom in this family. Tau accumulation and hypometabolism were observed prior to brain atrophy in mutation carriers. Plasma NfL and GFAP concentrations were elevated in the two svPPA patients. Some relative decreases and some relative increases in regional cerebral blood flow (CBF) as measured by arterial spin labelling (ASL) were observed in mutation carriers compared to noncarriers.

CONCLUSIONS

This study describes a large svPPA-affected family with the MAPT P301L mutation and provides an ideal model for inferring underlying pathology and pathophysiological processes in svPPA caused by tauopathies.

Clinical characteristics and genotype-phenotype correlation analysis of familial Alzheimer’s disease patients with pathogenic/likely pathogenic amyloid protein precursor mutations

Alzheimer’s disease (AD) is a progressive neurodegenerative disease associated with aging, environmental, and genetic factors. Amyloid protein precursor (APP) is a known pathogenic gene for familial Alzheimer’s disease (FAD), and now more than 70 APP mutations have been reported, but the genotype-phenotype correlation remains unclear. In this study, we collected clinical data from patients carrying APP mutations defined as pathogenic/likely pathogenic according to the American college of medical genetics and genomics (ACMG) guidelines. Then, we reanalyzed the clinical characteristics and identified genotype-phenotype correlations in APP mutations. Our results indicated that the clinical phenotypes of APP mutations are generally consistent with typical AD despite the fact that they show more non-demented symptoms and neurological symptoms. We also performed genotype-phenotype analysis according to the difference in APP processing caused by the mutations, and we found that there were indeed differences in onset age, behavioral and psychological disorders of dementia (BPSD) and myoclonus.

Current research status of blood biomarkers in Alzheimer's disease: Diagnosis and prognosis

Alzheimer's disease (AD), which mainly occurs in the elderly, is a neurodegenerative disease with a hidden onset, which leads to progressive cognitive and behavioral changes. The annually increasing prevalence rate and number of patients with AD exert great pressure on the society. No effective disease-modifying drug treatments are available; thus, there is no cure yet. The disease progression can only be delayed through early detection and drug assistance. Therefore, the importance of exploring associated biomarkers for the early diagnosis and prediction of the disease progress is highlighted. The National Institute on Aging- Alzheimer's Association (NIA-AA) proposed A/T/N diagnostic criteria in 2018, including Aβ42, p-tau, t-tau in cerebrospinal fluid (CSF), and positron emission tomography (PET). However, the invasiveness of lumbar puncture for CSF assessment and non-popularity of PET have prompted researchers to look for minimally invasive, easy to collect, and cost-effective biomarkers. Therefore, studies have largely focused on some novel molecules in the peripheral blood. This is an emerging research field, facing many obstacles and challenges while achieving some promising results.

Dementia in Southeast Asia: influence of onset-type, education, and cerebrovascular disease

Background

Southeast Asia represents 10% of the global population, yet little is known about regional clinical characteristics of dementia and risk factors for dementia progression. This study aims to describe the clinico-demographic profiles of dementia in Southeast Asia and investigate the association of onset-type, education, and cerebrovascular disease (CVD) on dementia progression in a real-world clinic setting.

Methods

In this longitudinal study, participants were consecutive series of 1606 patients with dementia from 2010 to 2019 from a tertiary memory clinic from Singapore. The frequency of dementia subtypes stratified into young-onset (YOD; <65 years age-at-onset) and late-onset dementia (LOD; ≥65 years age-at-onset) was studied. Association of onset-type (YOD or LOD), years of lifespan education, and CVD on the trajectory of cognition was evaluated using linear mixed models. The time to significant cognitive decline was investigated using Kaplan-Meier analysis.

Results

Dementia of the Alzheimer’s type (DAT) was the most common diagnosis (59.8%), followed by vascular dementia (14.9%) and frontotemporal dementia (11.1%). YOD patients accounted for 28.5% of all dementia patients. Patients with higher lifespan education had a steeper decline in global cognition (p<0.001), with this finding being more pronounced in YOD (p=0.0006). Older patients with a moderate-to-severe burden of CVD demonstrated a trend for a faster decline in global cognition compared to those with a mild burden.

Conclusions

There is a high frequency of YOD with DAT being most common in our Southeast Asian memory clinic cohort. YOD patients with higher lifespan education and LOD patients with moderate-to-severe CVD experience a steep decline in cognition.